Anthony Joshua, right, and Italy's Emanuele Leo pose during the weigh-in for the Briton's professional debut. Photograph: Andrew Couldridge/Action Images

It says something about Anthony Joshua's relaxed state of mind before his professional debut that, after spending an hour thoughtfully answering the media's questions, he spent nearly as long playfully arm-wrestling friends. No one mustered much of a challenge. You suspect his opponent on Saturday night, the Italian Emanuele Leo, will not either.

Leo's CV shows an unbeaten 8-0 record, but the physical disparity with Britain's Olympic super-heavyweight gold medallist was laid bare when their tops were removed at Friday's weigh-in. Both came in a shade over 16st 6lb, but so muscular and defined was Joshua's midsection that it could have been sculpted from marble. Leo's dough belly, meanwhile, owed rather too much to mamma's pasta.

However, Joshua is not taking anything for granted. After Audley Harrison won Olympic gold in Sydney his one-man hype-machine hyperventilated on its own hubris; Joshua stresses the need to learn and stay humble.

After shaking hands with Leo – something he always did with opponents in the amateurs – he insisted the fight would be just as important to him as his gold medal bout.

"This is a serious business," he said. "It's like the Olympic final for me. I'm going to be walking out in front of nearly 20,000 people and Leo has come to fight; he's got a winner's mentality. I've got to make sure I'm relaxed, perform to what I'm capable of and the win will come."

Leo appears resigned to his fate as a suitable sacrificial lamb who will test Joshua but not overextend him. The Italian admitted he had not watched Joshua and was not exactly talking up his chances of springing a surprise.

"I hope I will do a good fight and win," he said. He claims to have a decent jab and left hook. Questions about his chin, however, remain unanswered.

The same can be said about Joshua – whose rare blend of physique, power and light-footed nimbleness, as well as his Olympic gold medal, advertise his pedigree.

"I've never been knocked down in a fight," Joshua added. "The only time it happened was in the amateurs when I first went up to Sheffield and started training with elite fighters. It happens to everyone. Every heavyweight I face is going to have knockouts on their record. The main thing I've got to learn is not to take silly shots."

Joshua believes he has improved significantly since winning gold at London 2012. "I'm more comfortable in the ring," he said. "At the Olympics it was more determination and fitness that got me through my battles. Now I can stand close and slip, parry and counter. I'm a multi-dimensional boxer."

In the buildup to his debut he has received good luck messages from the Klitschko brothers, Wladimir and Vitali, who told him: "Good luck and welcome to the professional world", as well as David Haye, whom he describes as "a really cool guy", adding: "Some heavyweights are a bit standoffish but he's someone you can speak to for advice." In the future he hopes to spar with Wladimir, who fights the unbeaten Russian Alexander Povetkin on Saturday.

Joshua has also heard from Harrison, who wished him all the best with what lies ahead. "I've got a lot of respect for Audley," Joshua insisted. "There is a lot of negative energy towards him but it takes a man to get into the ring."

While Joshua should win with few scares or blemishes, Bury's WBA super-bantamweight world champion, Scott Quigg, faces a real battle against the unbeaten Cuban Yoandris Salinas – in what is likely to be the fight of the night. "I know what I am up against," Quigg said. "He's a very good fighter but I'm 100% confident."